Department of Animal Science - Plants Poisonous to Livestock

STEROID ALKALOIDS

Steroid alkaloids have a fairly complex nitrogen containing
nucleus. Two important classes of steroid alkaloids are

the Solanum type - one example is solanidine.
This steroid alkaloid is the nucleus (i.e. aglycone) for two important
glycoalkaloids, solanine and chaconine, found
in potatoes. Other plants in the Solanum family including various
nightshades, Jerusalem cherries, and tomatoes also contain solanum-type
glycoalkaloids. Glycoalkaloids are glycosides of alkaloids.

Solanum-type alkaloids are found in plants in the form of glycosides
of alkaloids. Glycosides are ethers that join a noncarbohydrate moiety
, the aglycone, by a ester bond to a carbohydrate moiety. In solanum-type
glycoalkaloids, the aglycone is a steroid alkaloid. Solanine and chaconine
cause poisoning in potatoes. They have the same aglycone,
solanidine, but the structure of their carbohydrate sidechains is different. Tomatine is a glycoalkaloid found in tomatoes. Its aglycone is tomatidine.

Where poisons are found

Production of solanum-type glycoalkaloids is favored by the
same conditions that promote the development of chlorphyll. Therefore,
the concentration of these glycoalkaloids is highest in potato sprouts
and green potato skins, and tomato vines and green tomatoes. Care should
be taken to prevent the exposure of potatoes to sunlight. These alkaloids
are not destroyed by cooking or drying at high temperatures. New potato
varieties can not be introduced unless they contain less than 20 mg glycoalkaloids/100
g.

*The glycoalkaloids are more poisonous than the steroid alkaloid
aglycones. Humans and all classes of livestock are susceptible to poisoning
by solunum- type glycoalkaloids. Luckily,

glycoalkaloids are poorly absorbed by the gastrointestinal
tract of mammals,

an appreciable amount of solanum-type glycoalkaloids is
hydrolized in the gut of mammals to the less toxic aglycones,

these metabolites are rapidly excreted in the urine and
feces of mammals. Because exposure to these poisons is generally by ingestion,
it takes a relatively large amount of them to cause death.